The present invention relates to an electrocardiogram (ECG) arrangement having m (m.gtoreq.2) lead channels for locating QRS complexes in an electrocardiogram and having a central logic unit.
As is known, in ECG examinations, it is becoming evermore frequent to use electrocardiogram arrangements having a plurality of lead channels which are usually fitted to the arms and legs (limb lead) and to the chest (chest lead). In the main, electrocardiogram arrangements which have twelve lead channels are available. There are, however, also electrocardiogram arrangements in which more or fewer than twelve lead channels are employed.
By way of example, for measuring heart rate or for analyzing arrhythmia, the redundancy involved with having multiple lead channels provides advantages when this redundancy is used to reduce or eliminate the effect of noise or artifacts in the result obtained using the electrocardiogram arrangement.
Previous electrocardiogram arrangements have exploited the multiple lead-channel redundancy and have collated the individual lead-channel signals by taking their first mathematical derivative. The individual mathematical derivatives are squared and then summed over all the lead channels. The square root of the result obtained in this way is then taken. The signal obtained in this way has the advantage that, compared with the individual original signals, the ratio of the useful signal component to the noise signal component is improved, which in the final analysis means that the QRS complexes can be located better.
Instead of squaring and taking the square root, sometimes only the magnitude of the signals given by the first mathematical derivative is calculated, this being followed by summing the magnitudes obtained for the individual lead channels.
In any event, with both electrocardiogram arrangements, the final result is a one-channel signal which is subjected to evaluation in relation to the QRS complexes.
The conventional electrocardiogram arrangements constructed in this way give reliable results if the level of noise is approximately the same in all the lead channels. However, if some of the lead channels have substantially stronger interference than other lead channels, which is often the case, for example, when recording a stress test electrocardiogram, it is expedient to exclude the signals from the very noisy lead channels from any subsequent processing.